Skip to content

Latest commit

 

History

History
147 lines (96 loc) · 6.66 KB

javascript-text.md

File metadata and controls

147 lines (96 loc) · 6.66 KB
title
JavaScript / Text Processing

JavaScript / Text Processing

String

  • String literals - Grammar and types - JavaScript | MDN

    • A string literal is zero or more characters enclosed in double (") OR single (') quotation marks. A string must be delimited by quotation marks of the same type; that is, either both single quotation marks or both double quotation marks. The following are examples of string literals:

      'foo'
"bar"
'1234'
'one line \n another line'
"John's cat"

    • You can call any of the methods of the String object on a string literal value—JavaScript automatically converts the string literal to a temporary String object, calls the method, then discards the temporary String object. You can also use the String.length property with a string literal:

      console.log("John's cat".length)
// Will print the number of symbols in the string including whitespace.
// In this case, 10.

    • In ES2015, TEMPLATE LITERALS are also available. Template literals are enclosed by the back-tick (` `) (grave accent) character instead of double or single quotes. Template strings provide syntactic sugar for constructing strings. This is similar to STRING INTERPOLATION features in Perl, Python and more.

      // Basic literal string creation
`In JavaScript '\n' is a line-feed.`

// Multiline strings
`In JavaScript template strings can run
 over multiple lines, but double and single
 quoted strings cannot.`

// String interpolation
var name = 'Bob', time = 'today';
`Hello ${name}, how are you ${time}?`

      Multiline 的用法是 template literal 特有的，雖然單雙引號搭配 escaped line break 也可以辦到，但就是沒那麼方便。

    • Optionally, a TAG can be added to allow the string construction to be customized, avoiding INJECTION ATTACKS or constructing higher level data structures from string contents. ??

      // Construct an HTTP request prefix used to interpret the replacements and construction
POST`http://foo.org/bar?a=${a}&b=${b}
     Content-Type: application/json
     X-Credentials: ${credentials}
     { "foo": ${foo},
       "bar": ${bar}}`(myOnReadyStateChangeHandler);

    • You should use string literals unless you specifically need to use a String object.

      應該是考量到可讀性，string literal 就會自動生成 String object，不用特別用 String(literal)。

    Using special characters in strings

    • In addition to ordinary characters, you can also include special characters in strings, as shown in the following example.

      'one line \n another line'

    • The following table lists the special characters that you can use in JavaScript strings.

      • \0 - Null Byte

      • \b - Backspace

      • \f - Form feed

      • \n - New line

      • \r - Carriage return

      • \t - Tab

      • \v - Vertical tab

      • \' - Apostrophe or single quote

      • \" - Double quote

      • \\ - Backslash character

      • \XXX

        The character with the Latin-1 encoding specified by up to three OCTAL digits XXX between 0 and 377. For example, \251 is the octal sequence for the copyright symbol.

      • \xXX

        The character with the Latin-1 encoding specified by the two HEXADECIMAL digits XX between 00 and FF. For example, \xA9 is the hexadecimal sequence for the copyright symbol.

      • \uXXXX

        The Unicode character specified by the four hexadecimal digits XXXX. For example, \u00A9 is the Unicode sequence for the copyright symbol. See Unicode escape sequences.

      • \u{XXXXX}

        Unicode code POINT ESCAPES. For example, \u{2F804} is the same as the simple Unicode escapes \uD87E\uDC04.

        這跟 \uXXXX 的用法有何不同 ??

    Escaping characters

    • For characters not listed in the table, a preceding backslash is IGNORED, but this usage is DEPRECATED and should be avoided.

    • You can insert a quotation mark inside a string by preceding it with a backslash. This is known as escaping the quotation mark. For example:

      var quote = "He read \"The Cremation of Sam McGee\" by R.W. Service.";
console.log(quote);

      The result of this would be:

      He read "The Cremation of Sam McGee" by R.W. Service.

      To include a literal backslash inside a string, you must escape the backslash character. For example, to assign the file path c:\temp to a string, use the following:

      var home = 'c:\\temp';

      You can also ESCAPE LINE BREAKS by preceding them with backslash. The backslash and line break are both removed from the value of the string.

      var str = 'this string \
is broken \
across multiple \
lines.'
console.log(str);   // this string is broken across multiple lines.

    • Although JavaScript does not have "HEREDOC" syntax, you can get close by adding a line break escape and an escaped line break at the end of each line:

      var poem =
'Roses are red,\n\
Violets are blue.\n\
Sugar is sweet,\n\
and so is foo.'

      ECMAScript 2015 introduces a new type of literal, namely template literals. This allows for many new features including multiline strings!

      var poem = 
`Roses are red, 
Violets are blue. 
Sugar is sweet, 
and so is foo.`

  • String | MDN #ril

String Interpolation ??

Multiline String ??

參考資料 {: #reference }

手冊：